Most people are aware that the prevalence of allergies, arthritis pain, influenza, and the common cold are affected by weather conditions. But weather can also influence the occurrence of other diseases, some of them life-threatening. These diseases can be divided into three major categories: insect-borne/rodent-borne, water-borne, and chronic.
Many diseases are transmitted by insects, including malaria, yellow fever, West Nile virus, plague, Rift Valley fever, and Lyme disease. Insect-control programs have eradicated some of these diseases from certain areas of the globe – for example, the mosquito-control program in Panama was essential to the building of the Panama Canal – but it has proven impossible to completely eliminate them. Even plague is still endemic in four U.S. states. These diseases often occur sporadically and are affected by weather patterns.
In east Africa, Rift Valley fever becomes a problem when heavy rains cause virus-infected mosquito eggs laid in damboes, depressions in the earth that are usually dry, to hatch and infect humans in the area. Similarly, in the salt marshes of Maryland, mosquito eggs carrying the Keystone virus hatch when flooding occurs, creating potential epidemics. Hurricanes are a common weather factor because of the heavy rains that accompany them, and emergency mosquito-control programs are often needed. Storm fronts, especially those that become stationary, will also drop heavy rains.
Temperature can also affect the development of insect-borne and rodent-borne diseases. A study in Portugal revealed that incidence of diseases such as leishmaniasis (sandflies), Lyme disease (ticks), and Mediterranean spotted fever (ticks) increased as temperatures climbed. Hantavirus Pulmonary Syndrome (HPS) increases during long seasons of warm weather in the Western United States, since the virus is tied to the deer mouse population. Lymphocytic choriomeningitis virus, carried by the house mouse and other rodents, may increase during colder temperatures if rodents move into housing areas to escape the cold.
Water-borne diseases are typically influenced by extremes of rainfall. Flooding from storm fronts, hurricanes, typhoons, and tsunamis can cause sewer systems to overflow, creating epidemics of diseases such as gastroenteritis (caused by e. coli and other agents), cholera, dysentery, hepatitis A, and typhoid fever. Many municipal sanitation systems in the U.S. are designed to overflow into local lakes or streams, but seepage into groundwater, streets, and parks can also occur. Developing countries which have little water sanitation are especially prone to these diseases, and flood events just make the problem worse.
Drought can also increase the risk of water-borne disease, since the concentration of disease-causing microorganisms is greater with regard to available water. The 2007 drought in the southeastern U.S. caused the water table and surface reservoirs in many areas to fall below critical levels, and residents were instructed to begin boiling water.
Finally, weather events can affect the prevalence and severity of chronic disease such as allergies, asthma, cardiovascular disease, and arthritis. Extremely hot weather is associated with increased risk of death from heart attack or chronic obstructive pulmonary disease (COPD). Cardiovascular disease (CVD) deaths in general occur more often on colder days. High pressure can cause pollution in the air to remain near the ground, triggering allergies, asthma, CVD and COPD. Many people report increased arthritis pain during changes in air pressure, particularly those associated with a surface front.
In recent years, global satellite monitoring has proven useful for tracking weather events, particularly in developing countries where ground monitoring is sparse, and subsequently forecasting possible disease outbreaks. The use of satellite and other weather and climate information has great potential in the area of public health.